Linux网络瑞士军刀 nc(netcat)

1.命令简介

nc（netcat）是一个短小精悍、功能实用、简单可靠的网络工具，主要有如下作用：

（1）端口侦听，nc 可以作为 server 以 TCP 或 UDP 方式侦听指定端口；

（2）端口扫描，nc 可以作为 client 发起 TCP 或 UDP 请求；

（3）机器之间传输文件；

（4）机器之间网络测速。

2.命令格式

nc [-46DdhklnrStUuvzC] [-i interval] [-p source_port] [-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_protocol] [-x proxy_address[:port]] [hostname] [port[s]]

常用选项：

• -4：只使用 IPv4 地址
• -6：只使用 IPv6 地址
• -l：启动本地监听
• -n：不使用 DNS 解析
• -p：指定源端口
• -s：指定源 IP 地址
• -u：使用 UDP，默认是 TCP
• -v：显示详细信息
• -w：设定超时时间（只适合用在 Client 端）
• -d：禁止从标准输入读取数据，也就是客户端输入数据不会发送到服务端
• -k：让服务端保持连接，不断开

3.常用示例

模拟服务端

nc -vkl 8080

模拟客户端

nc -v 127.0.0.1 8888

连接日志

#server
root@VM-16-3-ubuntu:~# nc -vkl 8080
Listening on 0.0.0.0 8080
Connection received on localhost 42930#client
root@VM-16-3-ubuntu:~# nc -v 127.0.0.1 8080
Connection to 127.0.0.1 8080 port [tcp/http-alt] succeeded!
#随后双方便可输入消息发送

发送文件

nc 不仅可以发送消息，还可发送文件。

假设服务端有一个 out.txt 的空文件，而客户端有一个 in.txt 文件，含有数据：hello server。

Server 端接收文件：

nc localhost 6000 > out.txt

Client 端发送文件：

nc localhost 6000 < in.txt

之后，我们可以看到 Server 端的 out.txt 文件中已经有数据了：

# cat out.txt
hello server

除了可以发送文件，nc 也可以发送目录，只需要将目录压缩发送即可。

端口扫码

端口扫描是一个非常重要的功能，很多时候系统管理员会通过扫描服务器上端口，来识别系统中漏洞，nc 工具提供了非常方便的操作：

nc -vz 127.0.0.1 1-100

这条命令扫描 192.168.1.3 上 1-100 端口区间，有哪些端口是开放的。

# nc -vz 127.0.0.1 1-100
nc: connect to 127.0.0.1 port 1 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 2 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 3 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 4 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 5 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 6 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 7 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 8 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 9 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 10 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 11 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 12 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 13 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 14 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 15 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 16 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 17 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 18 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 19 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 20 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 21 (tcp) failed: Connection refused
Connection to 127.0.0.1 22 port [tcp/ssh] succeeded!
nc: connect to 127.0.0.1 port 23 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 24 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 25 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 26 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 27 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 28 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 29 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 30 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 31 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 32 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 33 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 34 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 35 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 36 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 37 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 38 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 39 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 40 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 41 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 42 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 43 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 44 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 45 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 46 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 47 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 48 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 49 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 50 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 51 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 52 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 53 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 54 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 55 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 56 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 57 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 58 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 59 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 60 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 61 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 62 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 63 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 64 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 65 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 66 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 67 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 68 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 69 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 70 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 71 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 72 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 73 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 74 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 75 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 76 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 77 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 78 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 79 (tcp) failed: Connection refused
Connection to 127.0.0.1 80 port [tcp/http] succeeded!
nc: connect to 127.0.0.1 port 81 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 82 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 83 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 84 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 85 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 86 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 87 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 88 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 89 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 90 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 91 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 92 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 93 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 94 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 95 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 96 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 97 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 98 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 99 (tcp) failed: Connection refused
nc: connect to 127.0.0.1 port 100 (tcp) failed: Connection refused

可以看到，只有 22和80号端口是开放的。

总结

nc 通过在两台机器之间建立连接来完成很多网络功能，数据传输、网络连接、端口扫描等，也有助于我们进行网络调试，排查网络故障。